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\title {Only Phenomenal Expectations Connect Core Knowledge of Objects to Thought \\ Only Phenomenal Expectations Connect Core Knowledge of Objects to Thought}

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Only Phenomenal Expectations Connect Core Knowledge of Objects to Thought

s.butterfill@warwick.ac.uk

\def \ititle {Only Phenomenal Expectations Connect Core Knowledge of Objects to Thought}

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It's a wonderful thing to be at a conference where Liz Spelke and Mike Tomasello are both keynote speakers. Whereas it is tempting to see these two as defending diametrically opposed positions, I want to suggest in my talk, in effect, that these two thinkers’ views are actually complementary parts of a single story.

This talk is about two related questions. First, What is the nature of infants’ earliest cognition of physical objects? And, second, How do you get from these early forms of cognition to knowledge of simple facts about particular physical objects?

\section{Four- and Five-month-olds Can Track Briefly Occluded Objects}

There is a wide range of evidence that four- and five-month-olds can track briefly occluded objects. Such evidence comes from infants’ reactions to a range of different scenarios. Some scenrios involve a comparision between the number of objects \citep[e.g.][]{spelke:1995_spatiotemporal}, others involve infants’ abilities to track the causal effects of unperceived objects \citep[e.g][]{baillargeon:1987_object}, while others require infants to track properties such as the shape and size of unperceived objects \citep[e.g.][]{wang:2004_young}, or to remember the location of a hidden object \citep[e.g.][]{wilcox:1996_location}.

4- and 5-month-olds can track briefly occluded objects

scenario method source
1 vs 2 objects habituation Spelke et al 1995
one unperceived object constrains another’s movement habituation Baillargeon 1987
where did I hide it? violation-of-expectations Wilcox et al 1996
wide objects can’t disappear behind a narrow occluder violation-of-expectations Wang et al 2004
when and where will it reappear? anticipatory looking Rosander et al 2004

scenario	method	source
1 vs 2 objects	habituation	Spelke et al 1995
one unperceived object constrains another’s movement	habituation	Baillargeon 1987
where did I hide it?	violation-of-expectations	Wilcox et al 1996
wide objects can’t disappear behind a narrow occluder	violation-of-expectations	Wang et al 2004
when and where will it reappear?	anticipatory looking	Rosander et al 2004

I have described these findings as supporting a conclusion about tracking rather than about representing.

For a process to \emph{track} the path of an occluded object is for it to nonaccidentally depend in some way on the occluded object’s path: in an interesting but limited range of situations, changes to the object’s path will cause corresponding changes to how the process unfolds. Relatedly, to say that someone can track occluded objects is to say that there are processes in her (or otherwise appropriately involving her) which track the paths of some occluded objects.

The fact that four- and five-month-olds can track briefly occluded objects raises a question. How do they do this?

\section{A Hypothesis: Object Indexes Underpin Infants’ Abilities}

How do four- and five-month-olds track briefly occluded objects?

How? Object Indexes!

But what is an object index? Formally, an object index is ‘a mental token that functions as a pointer to an object’ \citep[p.\ 11]{Leslie:1998zk}. If you imagine using your fingers to track moving objects, an object index is the mental counterpart of a finger \citep[p.~68]{pylyshyn:1989_role}.

The interesting thing about object indexes is that a system of object indexes (at least one, maybe more) appears to underpin cognitive processes which are not strictly perceptual but also do not involve beliefs or knowledge states. While I can’t fully explain the evidence for this claim here, I do want to mention the two basic experimental tools that are used to investigate the existence of, and the principles underpinning, a system of object indexes which operates between perception and thought ...

Suppose you are shown a display involving eight stationary circles, like this one.

Then they stop and one of the circles flashes. Your task is to say whether the flashing circle is one you were supposed to track. Adults are good at this task \citep{pylyshyn:1988_tracking}, indicating that they can use at least four object indexes simultaneously.

(\emph{Aside.} That this experiment provides evidence for the existence of a system of object indexes has been challenged. See \citet[p.\ 59]{scholl:2009_what}: \begin{quote} `I suggest that what Pylyshyn’s (2004) experiments show is exactly what they intuitively seem to show: We can keep track of the targets in MOT, but not which one is which. [...] all of this seems easily explained [...] by the view that MOT is simply realized by split object-based attention to the MOT targets as a set.' \end{quote} It is surely right that the existence of MOT does not, all by itself, provide support for the existence of a system of object indexes. However, contra what Scholl seems to be suggesting here, the MOT paradigm can be adapated to provide such evidence. Thus, for instance, \citet{horowitz:2010_direction} show that, in a MOT paradigm, observers can report the direction of one or two targets without advance knowledge of which targets' directions they will be asked to report.)

Pylyshyn 2001, figure 6

There is a behavioural marker of object-indexes called the object-specific preview benefit. Suppose that you are shown an array of two objects, as depicted here. At the start a letter appears briefly on each object. (It is not important that letters are used; in theory, any readily distinguishable features should work.)

At the end of the task, a letter appears on one of the objects. Your task is to say whether this letter is one of the letters that appeared at the start or whether it is a new letter. Consider just those cases in which the answer is yes: the letter at the end is one of those which you saw at the start. Of interest is how long this takes you to respond in two cases: when the letter appears on the same object at the start and end, and, in contrast, when the letter appears on one object at the start and a different object at the end. It turns out that most people can answer the question more quickly in the first case. That is, they are faster when a letter appears on the same object twice than when it appears on two different objects \citep{Kahneman:1992xt}. This difference in response times is the % $glossary: object-specific preview benefit \emph{object-specific preview benefit}. Its existence shows that, in this task, you are keeping track of which object is which as they move. This is why the existence of an object-specific preview benefit is taken to be evidence that object indexes exist.

Kahneman et al 1992, figure 3

The \emph{object-specific preview benefit}: ‘observers can identify target letters that matched the preview letter from the same object faster than they can identify target letters that matched the preview letter from the other object’ \citep[p.\ 2]{Krushke:1996ge}.

In what follows I will take it for granted that, in adult humans, there is a system of object indexes which enables them to track potentially moving objects in ongoing actions such as visually tracking or reaching for objects, and which influences how their attention is allocated \citep{flombaum:2008_attentional}.

object indexes / files in adults and infants ...

guide ongoing action (e.g. visual tracking, reaching)
influence how attention is allocated

are subject to signature limits

The system of object indexes is also subject to signature limits. In general, a \emph{signature limit of a system} is a pattern of behaviour the system exhibits which is both defective given what the system is for and peculiar to that system.

One signature limit of a system of object indexes is that featural information sometimes fails to influence how objects are assigned in ways that seem quite dramatic. Let me illustrate ...

In this scenario, a patterned square disappears behind the barrier; later a plain black ring emerges. If you consider speed and direction only, these movements are consistent with there being just one object. But given the distinct shapes and textures of these things, it seems all but certain that there must be two objects. Yet in many cases these two objects will be assigned the same object index \citep{flombaum:2006_temporal,mitroff:2007_space}. So one signature limit of systems of object indexes is that information about speed and distance can override information about shape and texture.

To clarify terminology, I should say that whereas I’m talking about object indexes, researchers more typically interpret this research in terms of object files. I’m sticking to object indexes rather than object files for reasons of simplicity and caution. If you believe in object files then you can interpret what I’m saying as referring to object files. And if you have doubts about object files, you might still have reason to accept that a system of object indexes exists.

But our interest in object indexes stems from a hypothesis about four-month-old infants’ abilities to track briefly occluded objects. According to this hypothesis, these abilities depend on a system of object indexes like that which underpins multiple object tracking or object-specific preview benefits \citep{Leslie:1998zk,Scholl:1999mi,Carey:2001ue,scholl:2007_objecta}. What makes this hypothesis attractive?

... and there are is also a report of neural markers too \citep{kaufman:2005_oscillatory}.

(\citet{kaufman:2005_oscillatory} measured brain activity in six-month-olds infants as they observed a display typical of an object disappearing behind a barrier. They found the pattern of brain activity characteristic of maintaining an object index. This suggests that in infants, as in adults, object indexes can attach to objects that are briefly unperceived.)

There is evidence that, similarly, even 10-month-olds will sometimes ignore featural information in tracking occluded objects \citep{xu:1996_infants}.% \footnote{ This argument is complicated by evidence that infants around 10 months of age do not always fail to use featural information appropriately in representing objects as persisting \citep{wilcox:2002_infants}. In fact \citet{mccurry:2009_beyond} report evidence that even five-month-olds can make use of featural information in representing objects as persisting \citep[see also][]{wilcox:1999_object}. %they use a fringe and a reaching paradigm. NB the reaching is a problem for the simple interpretation of looking vs reaching! Likewise, object indexes are not always updated in ways that amount to ignoring featural information \citep{hollingworth:2009_object,moore:2010_features}. It remains to be seen whether there is really an exact match between the signature limit on object indexes and the signature limit on four-month-olds’ abilities to represent objects as persisting. The hypothesis under consideration---that infants’ abilities to track briefly occluded objects depend on a system of object indexes like that which underpins multiple object tracking or object-specific preview benefits---is a bet on the match being exact. }

Here are the results. The central column shows that infants looked longer when they saw two objects at test rather than when they saw a single object. This is not different from how they performed in a base line condition when the information about number was not present. And it is different from how they performed in the ‘spatiotemporal condition’ in which the two objects were at simultaneously visible at one point before the test phase.

The hypothesis has an advantage which I don’t think is widely recognised. This is that object indexes are independent of beliefs and knowledge states. Having an object index pointing to a location is not the same thing as believing that an object is there. And nor is having an object index pointing to a series of locations over time is the same thing as believing or knowing that these locations are points on the path of a single object. Further, the assignments of object indexes do not invariably give rise to beliefs and need not match your beliefs.

So assignments of object indexes can conflict with beliefs. Why is this an advantage?

At the start of this talk I emphasised the variety of evidence which shows that infants, from four months of age or earlier, can track briefly occluded objects. However there is also a substantial body of evidence which suggests that infants of this age, and even infants who are several months older, systematically fail to search for briefly occluded objects.

To illustrate, consider an ingenious experiment by \citet{Shinskey:2001fk}. There was an opaque screen that could rotate between lying flat on the ground and being raised to conceal a toy behind it. \citeauthor{Shinskey:2001fk} also used a second piece of apparatus just like the first except that the screen was transparent rather than opaque. They reasoned that infants would quite often pull the screen forwards just for fun, regardless of what is behind it. However, they also guessed that when infants know there is an interesting toy behind the screen, then they will pull it forwards more often than when they know that there is nothing behind the screen. This is just what happened when infants were presented with the apparatus involving a transparent screen: they sometimes pulled the screen forwards when there was no toy behind it, but they pulled it forwards significantly more often when the toy was behind it. What happened when infants were presented with the opaque screen? Here infants pulled the screen forwards no more often when they had observed a toy being placed behind it then when they had observed that there was nothing behind it. This is evidence that seven-month-old infants do not know that a toy they have very recently seen hidden behind a screen is behind the screen. After all, since knowledge guides action we would expect infants who know that a toy is behind an opaque screen to pull the screen forward more often than infants who know there is nothing behind the screen, just as they do when the screen is transparent.

More than two decades of research strongly supports the view that infants fail to search for objects hidden behind barriers or screens until around eight months of age \citep[p.\ 202]{Meltzoff:1998wp} or maybe even later \citep{moore:2008_factors}. Researchers have carefully controlled for the possibility that infants’ failures to search are due to extraneous demands on memory or the control of action. We must therefore conclude, I think, that four- and five-month-old infants do not have beliefs about the locations of briefly occluded objects. It is the absence of belief that explains their failures to search.

Because this point is controversial, I want to mention one further piece of the puzzle. Five-month-olds not only sometimes fail to search for hidden objects but also sometimes fail to look longer when a momentarily hidden object fails to reappear as if by magic. Infants will reach for an object hidden in darkness \citep[e.g.][]{jonsson:2003_infants}. But what happens if instead of measuring reaching we measure looking times? \citet{charles:2009_object} compared what happens when an object is momentarily hidden behind a screen with what happens when an object is momentarily hidden by darkness. They used a trick with light and mirrors so that for some of the infants, the object did not reappear when the screen came up or the light returned. Surprisingly, five-month-old infants’ looking times indicated that an expectation had been violated only when the object was hidden behind a screen but not when hidden by darkness.

I think this pattern of findings is good evidence against the hypothesis that four- or five-month-olds have beliefs about, or knowledege of, the locations of unperceived objects. After all, a belief is essentially the kind of state that can inform actions of any kind, whether they involve looking, searching with the hands or anything else.

So this is a virtue of the hypothesis that four- and five-month-old infants’ abilities to track briefly occluded objects depend on a system of object indexes. Since assignments of object indexes do not entail the existence of corresponding beliefs, the fact that infants of this age systematically fail to search for briefly occluded objects is not an objection to the hypothesis.

But the hypothesis does face a significant challenge ...

The primary functions of object indexes include influencing the allocation of attention and perhaps guiding ongoing action. If this is right, it may be possible to explain anticipatory looking directly by appeal to the operations of object indexes. But the operations of object indexes cannot directly explain differences in how novel things are to an infant. And nor can the operations of object indexes directly explain why infants look longer at stimuli involving discrepancies in the physical behaviour of objects.

We know that infants are likely to maintain object indexes for the two mice while they are occluded. Accordingly, when the screen drops in the condition labelled ‘impossible outcome’, there is an interruption to the normal operation of object indexes: infants have assigned two object indexes but there is only one object. But why does this cause infants to look longer at in the ‘impossible outcome’ condition than in the ‘possible outcome’ condition? How does a difference in operations involving object indexes result in a difference in looking times?

Here you see the results. The looking times are always over 10 seconds, and infants look more than a second longer (mean looking time) at the impossible event. How could the operations of object indexes cause this difference?

An initially appealing move would be to add would be beliefs. That is, it would be natural to say that assignments of object indexes give rise to corresponding beliefs, and these beliefs in turn explain facts about what appears novel or strange.% \footnote{ I guess many researchers do think that this, or something like it, is true. For instance, \citet{Leslie:1998zk} present their hypothesis as a view about infants’ object \emph{concept}. } But we’ve just seen that this view is almost certain to be wrong because it generates incorrect predictions about infants’ manual searching.

	occlusion	endarkening
violation-of-expectations	+	-
manual search	-	+

\section{Phenomenal Expectations Connect Object Indexes to Looking Durations}

object index operations

↓

? ? ? phenomenal expectations

↓

patterns in looking durations

So those who, like me, are impressed by the evidence for the hypothesis that four- and five-month-olds’ abilities to track occluded objects are underpinned by the operations of a system of object indexes are left with a question. The question is, What links the operations of object indexes to patterns in looking duration?

I’ve just argued that it can’t be beliefs or knowledge states.

Wynn 1992, fig 1 (part)

Recall this situation. Suppose you have seen it a hundred times before, so you know just what to expect. Still, the tendancy to expect two objects is on some level barely diminished, and event in which a single object is revealled is liable to feel magical in some small way. This feeling of magic is a phenomenal expectation.

Let me give you two more illustrations [the wire and the face]. ...

What is a phenomenal expectation? Consider a second illustration.

Here is a wire. Contrast two sensory encounters with this wire. In the first you visually experience the wire as having a certain shape. In the second you receive an electric shock from the wire without seeing or touching it.% \footnote{This illustration is borrowed from Campbell (2002: 133–4); I use it to support a claim weaker than his.} The first sensory encounter involves perceptual experience as of a property of the wire whereas, intuitively, the second does not. I take this intuition to be correct.% \footnote{ Notice that the intuition is not that the shock involves no perceptual experience at all, only that the shock does not involve perceptual experience as of any property of the wire. Notice also that the intuition concerns what a perceptual experience is as of, and not directly what is represented in perception. The relation between these two is arguably not straightforward (compare, e.g., \citet[p.~28]{Shoemaker:1994el} or \citet[pp.~50--2]{Chalmers:2006xq} on distinguishing representational from phenomenal content). }

The intuition is potentially revealing because the electric shock involves rich phenomenology, and its particular phenomenal character depends in part on properties of its cause (changes in the strength of the electric current would have resulted in an encounter with different phenomenal character). So there are sensory encounters which, despite having phenomenal characters that depend in part on which properties are encountered, are not perceptual experiences as of those properties.

What is a phenomenal expectation? Consider a third (and final) illustration.

Here is a face that I hope will seems familiar to most people. When you see this face, you have a feeling of familiarity. This feeling of familiarity is not just a matter of belief: even if you know for sure that you have never encountered the person depicted here (and trust me, you haven’t), the feeling of familiarity will persist. Nor is the feeling a matter of perceptual experience: you can’t perceptually experience familiarity any more than you can perceptually experience electricity.

(The face is a composite of Bush and Obama. It is chosen to illustrate that the feeling of familiarity is not a consequence of how familiar things actually are; instead it may be a consequnece of the degree of fluency with which unconscious processes can identify perceived items \citep{Whittlesea:1993xk,Whittlesea:1998qj}. Learning a grammar can also generate feelings of familiarity. Subjects who have implicitly learned an artificial grammar report feelings of familiarity when they encounter novel stimuli that are part of the learnt grammar \citep{scott:2008_familiarity}. They are also not doomed to treat feelings of familiarity as being about actual familiarity: instead subjects can use feeling of familiarity in deciding whether a stimulus is from that grammar \citep{Wan:2008_familiarity}.)

I could go on to mention the feeling you have when someone’s eyes are boring into your back, or the feeling that a name is on the tip of your tongue. But let me focus just on the feelings associated with electricity and with familiarity. These feelings are paradigm cases of phenomenal expectation.

All three examples (the feelings of magic, of electricity and of familiarity) show that:

There are aspects of the overall phenomenal character of experiences which their subjects take to be informative about things that are only distantly related (if at all) to the things that those experiences intentionally relate the subject to.

To illustrate, having a feeling of familiarity is not a matter of standing in any intentional relation to the property of familiarity, but it is something that we can interpret as informative about famility.

Phenomenal expecations

can be thought of as

sensations.

Phenomenal expectations can be thought of as sensations in approximately Reid’s sense.% \footnote{ \citet{Reid:1785cj,Reid:1785nz}. Even if you don’t believe that there are sensations in Reid’s sense, thinking of phenomenal expectations as if they were sensations will serve to illustrate their characteristic features. The main points that follow are consistent with several different ways of thinking about phenomenal expectations. For instance, you might take the view that what I am calling phenomenal expectations are perceptual experiences of the body or of bodily reactions, or that they involve some kind of cognitive phenomenology. The essential claim is just that the phenomenal expectations associated with the operations of object indexes are not constituted by states which involve intentional relations to any of the things which are assigned an object index. }

Sensations are

monadic properties of perceptual experiences
individuated by their normal causes
(so they do not involve an intentional relation)
which alter the overall phenomenal character of those experiences
in ways not determined by the experiences’ contents.

Sensations are: \begin{enumerate} \item monadic properties of events, specifically perceptual experiences, \item individuated by their normal causes% %{Tye, 1984 #1744@204} ---in the case of feelings of familiarity, its normal cause is ease of processing \item which alter the overall phenomenal character of those experiences \item in ways not determined by the experiences’ contents (so two perceptual experiences can have the same content while one has a sensational property which the other lacks). \end{enumerate}

Phenomenal expectations trigger beliefs only via associations.

An important consequence is that phenomenal expectations can lead to beliefs only via associations or further beliefs. They are signs which need to be interpreted by their subjects (\citealp[Essay~II, Chap.~16, p.~228]{Reid:1785cj} \citealp[Chap.~VI sect.~III, pp.~164–5]{Reid:1785nz}). Let me explain.

As a scientist, you can pick out the feeling of familiarity as that phenomenal expectation which is normally caused by the degree to which certain processes are fluent. But as the subject of who has that phenomenal expectation, you do not necessarily know what its typical causes are. This is something you have to work out in whatever ways you work out the causes of any other type of event.

(Contrast phenomenal expectations with perceptual experiences. Having a perceptual experience of, say, a wire’s shape, involves standing in an intentional relation to the wire’s shape; and the phenomenal character of this perceptual experience is specified by this intentional relation.% \footnote{ Compare \citet[p.~380]{Martin:2002yx}: ‘I attend to what it is like for me to inspect the lavender bush through perceptually attending to the bush itself.’ And \citet[p.~211]{byrne:2001_intentionalism} ‘subject can only discover the phenomenal character of her experience by attending to the world ... as her experience represents it.’ } Such perceptual experiences are often held to reveal the wire’s shape to the subject and so lead directly to beliefs.% \footnote{ Compare \citet[p.~222]{Johnston:1992zb}: ‘[j]ustified belief … is available simply on the basis of visual perception’; \citet[p.~143–4]{Tye:1995oa}: ‘Phenomenal character “stands ready … to make a direct impact on beliefs’; and \citet[p.~291]{Smith:2001iz}: ‘[p]erceptual experiences are … intrinsically … belief-inducing.’ })

(By contrast, having a phenomenal expectation concerning familiarity or an physical object’s path does not involve standing in any intentional relation to these things. The phenomenal expectation is individuated by its normal causes, rather than by any intentional relation. And a phenomenal expectation leads to belief, if at all, only indirectly. For learning is required in order for the subject to come to a view on what tends to cause the phenomenal expectation.)

Phenomenal expectations have been quite widely neglected in philosophy and developmental psychology. They are a means by which cognitive processes enable perceivers to acquire dispositions to form beliefs about objects’ properties which are reliably true. Phenomenal expectations provide a low-cost but efficient bridge between non-conscious cognitive processes and conscious reasoning.

object index operations

↓

phenomenal expectations

↓

patterns in looking durations

So my question was how the operations of object indexes might explain patterns of looking duration in habituation and violation-of-expectation experiments. My guess is that some operations of object indexes give rise to phenomenal expectations, which in turn influence looking durations.

object indexes
(= ‘core knowledge’)

↓

? ? ?

↓

knowledge of objects

\section{Development Is Rediscovery}

This guess gives rise to a further question (which I want to articulate but won’t attempt to answer). In asking how the operations of object indexes might give rise to patterns in looking duration, we have been concerned with what happens a short interval of time. But the guess about phenomenal expectations raises a question about the course of development in the first months or years of life. Let me explain.

In the beginning Spelke and others conjectured that infants’ abilities to track briefly occluded objects were a consequence of their having core knowledge for objects. This conjecture is related to the later hypothesis about object indexes. The idea is that we can further specify the mechanisms that realise infants’ core knowledge of physical objects by identifying it with a system of object indexes.

There was always a question about how infants’ core knowledge about objects might explain the emergence of knowledge knowledge (that is, knowledge proper) about objects. Now this question becomes, What is the role of a system of object indexes in the emergence in development of knowledge of physical objects? In short, How do you get from object indexes to knowledge?

Answers to these questions typically assume that core knowledge provides a conceptual identification of objects and some of their properties such as location or size, or else that it involves standing in some kind of intentional relation to these things. This is true of Spelke’s suggestion that mature understanding of objects, number, and mind derives from core knowledge by virtue of core knowledge representations being assembled \citep{Spelke:2000nf}; claims by Leslie and others that modules provide conceptual identifications of their inputs \citep{Leslie:1988ct}; Karmiloff-Smith’s representational re-description \citep{Karmiloff-Smith:1992lv}; and Mandler’s claim that ‘the earliest conceptual functioning consists of a redescription of perceptual structure’ \citep{Mandler:1992vn}.

But recall the guess about phenomenal expectations linking object indexes to patterns of looking duration. If this guess is right, then it is not true that core knowledge provides a conceptual identification of objects. And it is not true that having core knowledge involves standing in any kind of intentional relation to objects and their properties. This makes the question about development particularly difficult to answer.

It means that rather than assembing or redescribing representations, development must be a process of rediscovery.

The step from phenomenal expectations to knowledge is like the step from feeling electric shocks to understanding electricity. So coming to know simple facts about particular physical objects may begin with object indexes and the phenomenal expectations these give rise to, but it does not end there. Interpreting the phenomenal expectations may involve interacting with objects, learning to use tools, and perhaps interacting with others and objects simultaneously.

Coming to know facts about physical objects is a matter of rediscovering things already implicit in a system of object indexes. Some might object that development can’t require such rediscovery because it would be hopelessly inefficient to require things already encoded to be learnt anew. But rediscovery is an elegant solution to a practical problem. If you are building a survival system you want quick and dirty heuristics that are good enough to keep it alive: you don’t necessarily care about the truth. If, by contrast, you are building a thinker, you want her to be able to think things that are true irrespective of their survival value. This cuts two ways. On the one hand, you want the thinker’s thoughts not to be constrained by heuristics that ensure her survival. On the other hand, in allowing the thinker freedom to pursue the truth there is an excellent chance she will end up profoundly mistaken %(Malebranche?) or deeply confused %(Hegel?) about the nature of physical objects. So you don’t want thought contaminated by survival heuristics and you don’t want survival heuristics contaminated by thought. Or, even if some contamination is inevitable, you want to limit it. %So you want inferential isolation. This combination is beautifully achieved by giving your thinker a system or some systems for tracking objects and their interactions which appear early in development, and also a mind which allows her to acquire knowledge of physical objects gradually over months or years, taking advantage of interactions with objects as well as social interactions about objects—providing, of course, that the two are not directly connected but rather linked only very loosely, via phenomenal expectations.

conclusion

1. Four- and five-month-olds can track briefly occluded objects

2. How?

Object indexes! (System of object indexes = core system)

3. How could the operations of object indexes explain patterns in looking duration?

Beliefs (because systematic failures to search)

Phenomenal expectations!

4. Development is ...

... assembling core knowledge

... redescription

... rediscovery

\section{Conclusion}

To conclude, I started by mentioning the wide variety of evidence that four- and five-month-olds can track briefly occluded objects. This evidence raises the question, How do infants do that? On the leading, best supported hypothesis, four- and five-month-olds’ abilities to track briefly occluded objects depend on a system of object indexes like that which underpins multiple object tracking or object-specific preview benefits. This hypothesis also has the virtue of being consistent with the most straightforward explanation of why infants of this age (four- to five-months) and even older systematically fail to manually search for occluded objects. (The explanation is that they lack beliefs about the locations of objects.)

Accepting this hypothesis forces us to confront a question. How could the operations of object indexes explain patterns in looking duration? This question arises because facts about the operations of object indexes do not themselves straightforwardly imply anything about how things seem to infants, nor about what they believe.

The answer, I suggested, is phenomenal expectations. Much as there are phenomenal expectations associated with the ease or difficulty of processing a complex stimulus like a face or letter sequence, so also phenomenal expectations are associated with operations involving object indexes. These phenomenal expectations are not intentional relations to the phyiscal objects whose behaviours normally cause them. Instead they can be thought of as sensations in roughly Reid’s sense. So they are monadic properties of perceptual experiences which carry information about physical objects.

Importantly, phenomenal expectations (like sensations) require interpretation. In order to get from a phenomenal expectation to a belief you need to form a view about what the phenomenal expectation is a sign of. This requires learning, and your view can change as you learn more.

This has consequences for understanding the emergence in development of knowledge of physical objects. Such knowledge is probably a consequence of the (core) system of object indexes, but on the view I have been defending the two can be only indirectly related. Having core knowledge of objects is a matter of having a system of object indexes. The system can affect what you believe or know about objects only by way of phenomenal expectations. Gaining knowledge proper requires interpreting the phenomenal expectations, and so is in part a matter of rediscovering information already processed by your core systems.

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